It almost sounds like a native current bush, but they usually bloom earlier than this for me; and they're not usually big enough to be mistaken for a tree either.

Another possibility is a flowering hawthorne, that's probably a better one, actually.

http://dailytroll.com/?p=825

Not sure how to make two links, so you'll need to cut and paste to see this picture of the hawthorne.

Here is a link that might be useful: Picture of current flowering

Yes: probably hawthorn trees. Only part that doesn't fit is blackberry-like fruit.

Here is a link that might be useful: Google = crataegus laevigata